Courtesy of Wizards of the Coast (WotC) and Ally Warfield, take a look at Core Set 2021‘s newest counterspell for one blue mana — Miscast.
Counter target instant or sorcery spell unless its controller pays 3.
A new take on situational counters for one blue mana, Miscast diverts from Spell Pierce, by taking away the chance to hit any non-creature spell, but making the payment three instead of two. Great for fighting on the stack against more than just instants like Dispel, Miscast offers a bit more versatility than Mystical Dispute by being able to hit non-blue spells for one.
Where exactly Miscast will fit in is still up in the air, but it clearly is a knockout against the Ultimatums from Ikoria and other expensive sorcery spells like Casualties of War, Command the Dreadhorde, and Finale of Devastation going for a knockout blow. In eternal formats it has to compete with Flusterstorm, Spell Pierce, and Dispel. If nothing else, Miscast gives blue mages even more options when crafting the right suite of counterspells.